Bret Contreras has an article up at Wannabebig called "Deadlift 5 Plates Like a Champion."
How heavy is that? 5 x 45 pound plates per side, plus the bar at 45 pounds equals 495 pounds.
Why do I want to check this out? Bret Contreras is very thorough in his articles, and has dissected the possible weak points in the deadlift, and thus what you need to fix to do one heavier than you do now. They are item by item - a stall where means what? What do I need to strengthen? How do I strengthen that, specifically?
Jungledoc suggested this on the EXRX forums, and I've read it and re-read it a number of times. If you're deadlifting and the numbers are stalling, check this out and see why and where. If you're a relative beginner and the deadlift is still just going up, you can wait on the advice, but it's still a good read. Skin-scraping fun for the whole deadlifting family.
Warning - you'll need to click "X" on an box offering you the (free) Wanna Be Big newsletter. Up to you if you want to join or not, but be ready for it when you click the link.